From Motors and Drives
Control of Speed and Torque
The speed of a DC motor is a direct result of the voltage applied. As indicated earlier, the DC motor requires two separate circuits to generate motor torque.
Control of Speed
The field receives voltage from a separate power supply, sometimes referred to as a field exciter. This exciter provides power to the field, which in turn generates current and magnetic flux. In a normal operating state, the field is kept at maximum strength, thereby allowing the field winding to develop maximum current and flux. This condition is known as opera-
tion in the armature range. (The only way to control the speed is through change in armature voltage.)
The armature power supply applies voltage to the armature through the brushes and the commutator. Basically, the greater the amount of voltage applied, the faster the speed of the motor. We can see this relationship in the formula below:
|S||=||speed in rpm|
|Ra||=||resistance of the armature|
|K1||=||motor design constant|
|φ||=||strength of the field flux|
As seen in the formula, if the...
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